Sound - Ultrasonic Materials Testing Technology Research

Acousto Ultrasonic (AU) is a new dynamic non-destructive evaluation method. It can provide the detailed information about the materials by analyzing the acquired signals that have passed through defects, failures or damages of structure. The research concentrated on the application of Acousto Ultrasonic (AU) techniques for the bond quality of adhesively bonded composite joints.Aimed at the application of the new techniques, an Acousto Ultrasonic detecting and analyzing system of composite has been established in this paper, including ultrasonic pulse card, data acquisition card,signal sampling and processing, and determining the final result. With this system, the honeycomb sandwich construction and fiber reinforced composite plates were regarded as study object and the features of the Acousto Ultrasonic signal would be studied by applying the signal processing method, such as spectrum analysis and wavelet analysis. By integrating conventional Fourie transformation with the smooth average method of spectrum, the high frequency noise was not only removed, but also the signal was smoothed and the main frequency of the signal was found easily and then was extracted as the coarse features of the signal. On the basis, in order to analyze the detail features of the signal, the signal can be decomposed using the db6 mother wavelet function. The experiments of wavelet analysis can indicate that the third frequency band described the main features of the signals completely. The wavelet coefficient of the feature band was regarded as the feature parameter of the Acousto Ultrasonic signal and it can distinguish defects from the adhesively bonded joints. Experiments showed that the method was effective and the results were in good agreement with the theory.